This invention relates to the radio frequency communication art and, more particularly, to a multiport, stripline radio frequency signal coupler.
Stripline couplers are well known in the radio frequency communication art. A common use for such couplers is the splitting of one RF signal into two or more signals. Using a similar approach, independent RF signals may be combined, or added via couplers.
A particularly useful coupler building block is the hybrid coupler. The hybrid coupler is comprised of a pair of adjoining metallizations deposited on a common substrate. The metallizations act as a transmission line at RF frequencies whereby signals may be applied at either ends of the metallizations to produce combining signals at the metallizations'free ends.
In many applications it is necessary that a plurality of hybrid couplers be interconnected. One such system is the eight port quadrature coupler wherein each of four independent input RF signals may be split into four equal parts, with each part appearing at one of the output ports. A further feature of the quadrature coupler is that each part of the divided input signal is phase shifted whereby the output ports, when taken in the proper order, are in phase quadrature.
In the prior art it has been known that an eight port quadrature coupler may be fabricated by interconnecting four hybrid couplers with coaxial cable. This results in a cumbersome, difficult to manufacture, and relatively expensive system. Moreover, since it is essential for proper operation of the coupler that all interconnecting electrical lengths between the hybrids be identical, such prior art couplers have been subject to performance degradation due to the required close tolerances.